Method of producing unitary nitrocellulose grains capable of fragmentation under primer blast to original granules



United States Patent METHOD 0F PRGDUCING UNITARY NEUTRO- QELLULOSE GRAENS CAPABLE OF FRAGMEN- TATION UNDER PRIMER BLAST T0 ORIGRNAL GRANULES Ralph L. Cook, Alton, Ill., assignor to Olin Mathieson Chemical Corporation, East Alton, lll., a corporation of Virginia No Drawing. Filed Sept. 30, 1960, Ser. No. 59,521

2 Claims. (ill. 149-2) This invention relates to explosives and particularly to a method of molding granular propellent powder grains into consolidated charges in which the identity of the individual grains is maintained.

Smokeless powder charges have traditionally been used as the propellent charge in small arms ammunition and also in artillery ammunition, the size of the grains increasing with the size and weight of the cartridge. Various attempts have previously been made to provide propellent powder charges as a unitary mass so as to avoid handling and packaging of the individual granules and to obviate the need of cartridge cases. The conventional round of ammunition consists of a cartridge case, a pro jectile, and a primer, the chief function of the cartridge case being that of confining the powder. One of the major needs, particularly in military ammunition, is for a round of ammunition in which the case is completely eliminated. This could readily be accomplished by the provision of a self-sustaining consolidated charge of propellent having a projectile secured to one end thereof and a primer to the other. However, such ammunition has not heretofore become a reality because of the inadequacy of previously prepared consolidated powder charge-s.

More recently, smokeless powder charges have also been used as components in gas generating cartridges. They are particularly useful as ignition and booster charges for transmitting the flame from the primer to the main charge. In such capacities, they must be functionally located with relation to the other components of the gas generating device. To obtain such positioning, the propellent powder grains are normally supported by some structural means such as trays, bags, combustible containers, and the like. Thus, the limitations on the utility of loose granular propellent charges has long been recognized and it has also been realized that these limitations could be minimized or substantially reduced by the provision of a consolidated self-contained powder charge that could be handled as a unit but would have the ballistic properties of a granular propellent.

Prior to the present invention, processes for such consolidation of propellent powder granule-s have met with only a modicum of success. These previous attempts have involved the application of pressure to substantially dry powder or to powder mixed with a solvent. The prior art dry molding methods were unsuccessful because the molded powder charges thus prepared had little or no cohesion and crumbled readily. While some success has been attained by consolidating powder grains wet with a solvent, such processes have a number of inherent disadvantages. They require the use of flammable solvents and rely for this success upon the uniform distribution of the solvent throughout the charge of powder grains followed by removal of the solvent. When particular care is not taken to insure uniform solvent distribution, the charges obtained are not uniform and upon combustion cannot burn as a normal progressive burning granular propellent charge.

It is, therefore, an object of this invention to provide a new and novel method for consolidating granular propellent charges that overcomes the disadvantages of the prior art processes. Another object of this invention is to provide a process of making consolidated propellent charges having the ballistic properties of a granular pro pellent charge. A more specific object of this invention is to provide a process of making consolidated propellent powder charges in which the identity of the individual particles making up the charge is maintained. A further object is to provide such a consolidated charge which is resolved to its individual component powder grains by the shock of an ammunition primer.

These and other objects are accomplished in accordance with this invention generally speaking by incorporating a sufficient amount of a liquid relatively non-volatile plasticizer into a charge of smokeless powder base propellent grains to render them tacky and then subjecting the charge to pressure so as to consolidate it into a unitary one-piece mass in which the identity of the individual granules is maintained. The physical structure of the consolidated mass can well be likened to fritted glass or sintered metal objects. The plasticizer employed to render the grains tacky can be mixed with the powder base prior to formation of the individual grains, or can be impregnated into the powder grains after their formation. Likewise, a portion of the plasticizer can be mixed with the smokeless powder propellent base prior to graining and the balance added by impregnating them with a sufiicient amount of the same or a compatible plasticizer to bring the plasticizer content to the required level.

Standard molding operations and apparatus can be used in compacting or consolidating the granular propellent charge of the present invention. For most operations, it is preferred to consolidate the charge under a pressure of about 3,000 to 5,000 pounds per square inch for a period of about 10 seconds to 1 minute. However, the pressure can vary between about 1,000 and 10,000 pounds per square inch with molding times varying from about 1 second to several minutes, depending upon the particular type of powder being consolidated and the size and shape of the final product. The consolidating operation is preferably carried out at ambient or room temperatures but can be executed at any temperature, not having any adverse efiect on the stability of the product. After the powder charge has been compacted it is only necessary to remove it from the mold. No further operation, such as solvent removal is entailed.

Powder grains of any desired shape can be utilized as the starting material for the manufacture of consolidated charges in accordance with this invention. The particular shape of the grains employed will depend to some extent upon the type of charge desired. While extruded or disc powder grains can be used, it is preferred to employ spherical powder grains of the type described in U.S. Patent 2,160,626, issued to Harold Schaefer. When such spherical grains are rolled and partially flattened, they provide a particularly advantageous starting material for the process of the present invention. The powder grains can be formed of any of the conventional gelatinizable bases. These bases include, for example, gelatinized nitrocellulose, nitrocellulose and nitroglycerine, nitrocellulose with accelerators and/ or deterrents, polyvinyl nitrate, nitrostarch and other gelatinizable polynitro compounds. It will also be understood that the powder used in the present process can contain the conventional stabilizers, modifiers and other constituents.

The propellent powder grains used in making the consolidated unitary charge can be incorporated with any of the ordinary liquid plasticizers for the propellent powder base. Thus the grains can be impregnated with a deterrent, an energizer, or a mixture of one or more energizers with one or more deterrents. Suitable energizing modifiers include nitroglycerine, butane triol trinitrate, diglycol dinitrate, ethylene glycol dinitrate, and the like.

The relatively non-volatile liquid deterrents that can be used in accordance with the present invention include dibutyl phthalate, dimethyl sebacate, dibutyl succinate, dibutyl adipate, triacetin, ethyl diphenyl phosphate, tributyl phosphate, and the like. Likewise, normally solid deterrents such as dimethyl phthalate, dioctyl sebacate, ortho nitro biphenyl, butyl benzyl phthalate, octyl diphenyl phosphate, triethylene glycol di-2-ethyl butyrate (i.e. triglycol dihexoate), and the like can be used in combination with the liquid modifiers with which they have been combined to provide a liquid mixture. lso such solid materials can be used alone but are generally not preferred because of the relatively high pressures and temperatures required in the molding operation.

The amount of modifier incorporated into the propellent powder grains prior to the molding operation has a considerable influence on the physical characteristics of the final product. The modifier content of the powder could be made sufiiciently large so that the grains lose their identity when subjected to molding conditions. On the other hand, the amount of modifier must be maintained at a sufficiently high level so as to insure the formation of a single grain that can be readily handled without physical failure. It has been found that the modifier content of the propellent powder charge must be at least about 20% and not greater than about 50% to insure the formation of a satisfactorily consolidated propellent charge.

The manner in which the objects of the present invention are achieved will be more readily apparent from the following specific example of a preferred embodiment thereof. In this example, and throughout the specification, all proportions are expressed in parts by weight.

Spherical propellent powder grains were prepared in accordance with the process described in U.S. 2,160,626. These grains consisted predominantly of nitrocellulose having a nitrogen content of about 13.2% and contained about 1% diphenylarnine. The spherical grains were of such a size that they passed through a screen having openings of about 0.025 inch and were retained on a screen having openings of 0.020 inch. The powder was then suspended with agitation in an excess of water, to which a solution of nitroglycerine was added in the conventional manner. The suspension was maintained until the nitroglycerine content of the powder grains was approximately 40%. The grains were then removed from the suspension and flattened by passing them between rollers, thus providing the grains with a web of about 0.007 inch. Charges of the rolled powder were prepared, each charge weighing approximately 3.2 grains each. The charges were placed in a press at room temperature and subjected to a ram pressure of approximately 4,000 pounds per square inch for about one minute to form consolidated propellent pellets having a diameter of approximately 0.020 inch. The resulting pellets were charged into primed caliber .38 Special cartridges and the mouth of the cartridges closed with conventional projectiles. The cartridges thus loaded were fired and the pressure and velocity of subject charges were compared with similar cartridges in which the consolidated charge was employed with the same weight of rolled unconsolidated grains. The pelleted material, upon firing, gave an average pressure of 13,700 pounds per square inch and a velocity of 811 feet per second. These results were quite similar to those obtained on firing the cartridges loaded with a loose charge of the same weight and composition. The loose charges in the same ammunition yielded a pressure of 14,500 pounds per square inch and a velocity of 329 feet per second. These results clearly illustrate that the ballistic results of the consolidated powder charge were equivalent to those of the granular product used in making up the charge. Such equivalent results could not be obtainable unless the grains making up the consolidated charge burned as individual particles. Thus, it is shown that the charges of the present invention when subjected to the blast of conventional primers fragment to provide the uniform burning characteristics of a conventional loose powder.

While the above example is concerned primarily with the preparation of consolidated charges in the form of pellets, it will be readily appreciated that the charges can be made of any convenient size or shape. Also, the consolidated charges can be readily employed as evanescent closures for various types of explosive and gas generating devices. This invention also contemplates the formation of self-contained propellent charges. In accordance with this modification, the conventional cartridge case can be dispensed with and the projectile and priming means connected to opposite ends of the charge. In addition, the physical strength of the consolidated charges of the present invention can be enhanced by coating them with a propellent powder base lacquer.

From the above description, it is clear that this invention accomplishes its objects and provides a novel process for producing a consolidated powder charge having the ballistic properties of a granular propellent.

Having now described the invention, what is claimed is:

1. A method for preparing a one-piece propellent powder charge which burns as a granular nitrocellulose propellent which comprises admixing nitrocellulose powder grains with a non-volatile liquid plasticizer selected from the group consisting of nitroglycerine, butane triol trinitratc, diglycol dinitrate, ethylene glycol dinitrate, dibutyl phthalate, dimethyl sebacate, dibutyl succinate, dibutyl adipate, triacetin, ethyl diphenyl phosphate, and tributyl phosphate, until said nitrocellulose powder grains contain between about 20 percent and about 50 percent by weight of said liquid plasticizer, separating the resulting nitrocellulose powder grains from excess liquid plasticizer, and subjecting the grains to a pressure between about 1,000 and about 10,000 pounds per square inch at ambient temperature until the grains adhere together to form a consolidated body of individual grains, said body being capable of fragmenting into individual grains when subjected to a primer blast.

2. The process of claim 1 wherein said liquid plasticizer is nitroglycerine.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR PREPARING A ONE-PIECE PROPELLENT POWDER CHARGE WHICH BURNS AS A GRANULAR NITROCELLULOSE PROPELLENT WHICH COMPRISES ADMIXING NITROCELLULOSE POWDER GRAINS WITH A NON-VOLATILE LIQUID PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF NITROGLYCERING BUTANE TRIOL TRINITRATE, DIGLYCOL DINITRATE, ETHYLENE GLYCOL DINITRATE, DIBUTYL PHTHALATE, DIMETHYL SEBACATE, DIBUTYL SUCCINATE, DIBUTYL ADIPATE, TRIACETIN, ETHYL DIPHENYL PHOSPHATE, AND TRIBUTYL PHOSPHATE, UNTIL SAID NITROCELLULOSE POWDER GRAINS CONTAIN BETWEEN ABOUT 20 PERCENT AND ABOUT 50 PERCENT BY WEIGHT OF SAID LIQUID PLASTICIZER, SEPARATING THE RESULTING NITROCELLULOSE POWDER GRAINS FROM EXCESS LIQUID PLASTICIZER, AND SUBJECTING THE GRAINS TO A PRESSURE BETWEEN ABOUT 1,000 AND ABOUT 10,000 POUNDS PER SQUARE INCH AT AMBIENT TEMPERATURE UNTIL THE GRAINS ADHERE TOGETHER TO FROM A CONSOLIDATED BODY OF INDIVIDUAL GRAINS, SAID BODY BEING CAPABLE OF FRAGMENTING INTO INDIVIDUAL GRAINS WHEN SUBJECTED TO A PRIMER BLAST. 